© 2003 BMJ Publishing Group
LETTER
Generalised estimating equations and low back pain
1 Arthritis Research Campaign Epidemiology Unit, Stopford Building, Medical School, University of Manchester, Oxford Road, Manchester M13 9PT, UK; moeyjefh@fs1.ser.man.ac.uk
2 Biostatistics Group, Medical School, University of Manchester
Keywords: back pain; estimating equations
| The first 150 words of the full text of this article appear below. |
We read with interest the article by Hoogendoorn et al who examined the use of different approaches to analysing data from their prospective cohort study of work related exposures and the future onset of low back pain.1
Exposures and outcomes are time dependent factors as they are subject to change over time. The strength of the relation depends on the assumptions of time dependence (or independence) of exposures and outcomes. The effects of these assumptions can be investigated by adopting different modelling approaches to studies that have collected repeated measures of exposure and outcome data over time.
Hoogendoorn et al have adopted such an approach in their study of work related risk factors for low back pain.1 Information on work related physical and psychosocial factors and low back pain outcome was collected at baseline and in three annual follow ups. They showed an increased risk of low back pain for
3 Netherlands Cancer Institute, Plesmanlaan 121 Amsterdam, Netherlands; l.hoogendoorn@nki.nl
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